Various processes useful to render the polymers flameproof are already known from the Art; these processes essentially consist in adding to the polymers thermally unstable halogenated compounds that decompose in consequence of heat under formation of hydrochloric or hydrobromic acid.
Some examples of such halogenated compounds are chlorinated paraffin waxes containing 40 to 75% of chlorine, and chlorinated or brominated phenols.
When halogenated compounds of the type of the aforesaid chlorinated paraffin waxes or of the type of the chlorinated or brominated phenols are added to polyethylene or polypropylene, the polymer combustibility undergoes a reduction that depends on the amount of halogen present in the polymer. To attain a satisfactory uninflammability degree, however, very high amounts of halogenated compounds, generally higher than 30% by weight with respect to the polymer, are required.
It is known how to reduce the amount of halogenated additive by introducing also an oxygen containing antimony compound of the type of trioxide or of antimony oxyhalides into the polymers.
Although the antimony trioxide+ halogenated paraffin compounds yield satisfactory results as regards the self-extinguishing properties, they are not free from very serious drawbacks. When antimony trioxide is used as a flame-extinguishing agent, it is usually added to the polymer in an amount higher than 10% by weight and halogenated paraffin as a flame-extinguishing agent is generally in an amount of 15-30% by weight, so that the total additive amount (antimony compound+ halogenated paraffin) is generally between 30 and 35% by weight with respect to the polymer. This brings about a strong deterioration of the polymer's mechanical properties (tensile strength, yield strength, hardness, resilience), a corrosion of the equipments in which the treatment is carried out and, finally, a strong evolvement of toxic smokes and gases in case of fire.
We have now surprisingly found particular flame-extinguishing agents for polymers and especially for polyolefins that reduce many of the drawbacks of the presently used flame-extinguishing agents mentioned above, particularly with respect to the total amount of additive required.